Sjögren's syndrome. Autoimmune epithelitis.

Sjögren's syndrome is a chronic autoimmune disorder characterized by mononuclear cell infiltration proximally to epithelial cells of exocrine glands. In recent years, several studies have tried to address the function of the components of the immunopathologic lesion in Sjögren's syndrome. The majority of the mononuclear infiltrating cells are CD4 positive T lymphocytes (60-70%) whereas B cells constitute one fourth of the infiltrating cells. Macrophages and natural killer cells are poorly represented in the lesion. Epithelial cells of minor salivary glands of patients with Sjögren's syndrome express proinflammatory cytokines (IL-1 beta, IL-6), protooncogenes (c-myc) and costimulatory molecules (B71, B72). The destruction of epithelial cells of Sjögren's syndrome patients is probably due to activation of several apoptotic pathways since epithelial cells express different apoptosis related molecules such as Fas, FasL, Bax, while mononuclear cells express Bcl-2, Perforin and Granzymes. Finally epithelial cells seem to exert a regenerative effort since they express trefoil proteins (pS2). The above properties give epithelial cells a significant role in the pathophysiology of the syndrome but the exact events which drive the immune system towards an autoimmune reaction remain obscure.

CD4 cytotoxic and dendritic cells in the immunopathologic lesion of Sjögren's syndrome.

The existence of CD4+ T lymphocytes with cytotoxic activity in minor salivary gland (MSG) biopsies from Sjögren's syndrome (SS) patients was investigated using in situ double immunohistochemistry technique. The presence of dendritic cells (DC) in SS lesions was examined by using single and double immunohistochemistry methods and a panel of different MoAbs to specific cell surface markers (i.e. CD3, CD11c, DRC). Furthermore, the ultrastructural morphology of DC was characterized by electron microscopy (EM). Immunogold labelling technique using the DRC surface marker was also applied. Finally, we investigated the existence of germinal centres (GC) in the salivary gland lesions of SS patients. Seven patients with primary SS and five patients with non-specific sialadenitis were the subjects of this study. Our results indicate the existence of a CD4+ cytotoxic cell population that utilizes perforin-mediated cell destructions as they expressed perforin mRNA. Quantitative analysis of these cells revealed that they comprised approximately 20% of the existing T lymphocytes. We also identified a population of CD4+ T cells that expressed the CD11c activation marker. Furthermore, we observed a distinct cell subtype which expressed the DRC cell surface marker. These cells had the characteristic ultrastructural morphology of DC and were DRC+ when examined by immunoelectron microscopy. Finally, the formation of GC structures in the histopathologic lesions of the salivary glands was observed. The above findings indicate that both CD4+ cytotoxic T lymphocytes (CTL) and DC may be involved in the initiation and perpetuation of SS pathogenesis. Moreover, the formation of GC in the lesions reveals a possible mechanism for in situ differentiation and proliferation of activated B lymphocytes.

Lymphoma development in Sjögren's syndrome: novel p53 mutations.

OBJECTIVE: Sjögren's syndrome (SS) is a chronic autoimmune disease characterized by lymphocytic infiltrations of the exocrine glands. Disease progression may lead to uncontrolled clonal proliferation of B lymphocytes and development of lymphoma. This study was undertaken to examine the possible involvement of the cell cycle checkpoint genes p53 and p21 in the pathophysiology of the syndrome. METHODS: Protein expression of p53 and p21 was studied, by immunohistochemistry and Western blot analysis, in minor salivary gland (MSG) biopsy specimens from 7 patients with SS and 5 control subjects. In addition, sequence analysis of the p53 gene was performed on DNA samples obtained from MSG biopsy samples of the same 7 patients with SS and from 4 patients with SS and in situ non-Hodgkin's lymphoma (NHL). RESULTS: The study revealed increased protein expression of p53 and p21 in MSG biopsy specimens from patients as compared with controls, while sequence analysis showed that the p53 gene was of the wild type. Furthermore, sequence analysis of the p53 gene from patients with SS and in situ NHL revealed 2 novel mutations in exon 5 of the p53 gene. These mutations are single-base substitutions and appear to be functional since exon 5 is included in the coding region of the p53 gene. CONCLUSION: This is the first report on wild-type p53 gene activation in SS. Our findings indicate a probable role for the DNA damage response genes in the pathogenesis of this syndrome. The novel mutations of the p53 gene implicate dysregulation of this tumor suppressor gene as a possible mechanism for lymphoma development in SS.

Modes of epithelial cell death and repair in Sjögren's syndrome (SS).

We evaluated possible modes of epithelial cell destruction and restoration in minor salivary gland biopsies from patients with SS. Minor salivary gland biopsies from 10 primary Sjögren's syndrome (pSS) patients and eight control individuals were evaluated by immunohistochemical staining for the expression of apoptosis-related molecules, substances released by activated cytotoxic T cells, as well as proteins involved in epithelial cell repair. The results were analysed by computer screen analysis and they were expressed as average percentages. Apoptosis-promoting molecules, Fas antigen and Fas ligand were observed in ductal and acinar epithelial cells as well as in infiltrating mononuclear cells of minor salivary glands from SS patients in comparison with control biopsies. Bax protein, which acts as a death-promoter message, was expressed in the ductal and acinar epithelial cells and in mononuclear infiltrating cells of SS patients compared with control individuals, while Bcl-2, an inhibitor of apoptosis, was primarily found in the lymphocytic infiltrates. In situ DNA fragmentation assay (TUNEL) revealed that epithelial cells were apoptotic in patients with SS compared with control subjects. Immunohistochemical staining for perforin and granzyme B, released from granules of activated cytotoxic lymphocytes, revealed their presence in lymphocytic infiltrates of patients with SS compared with control biopsies. pS2, a member of the trefoil protein family which functions as promoter of epithelial cell repair and cell proliferation, was expressed in epithelial cells in biopsies from SS patients. These studies suggest that the functional epithelium of minor salivary glands in patients with SS appears to be influenced by both intrinsic and extrinsic mechanisms of destruction, while a defensive mechanism of epithelial restoration seems to be active.

Immunopathology of Sjögren's syndrome.

Sjögren's syndrome is a chronic autoimmune disorder characterized by mononuclear cell infiltration around epithelial cells of exocrine glands. In recent years, several studies have tried to elucidate the components of the immunopathologic interaction in Sjögren's syndrome as well as the function of these components. The majority of the mononuclear infiltrating cells are CD4 positive T lymphocytes (60-70%) whereas B cells constitute one fourth of the infiltrating cells. Macrophages and natural killer cells are poorly represented in the lesion. Epithelial cells of minor salivary glands of patients with Sjögren's syndrome express several cytokines (IL-1 beta, IL-6, NO), protooncogenes (c-myc), autoantigens (Ro, La, Fodrin) and costimulatory molecules (B71, B72). The characteristic destruction of epithelial cells of Sjögren's syndrome patients is probably due to activation of several apoptotic pathways since epithelial cells express different apoptosis related molecules such as Fas, FasL, Bax, while mononuclear cells express Perforin and Granzymes. Finally epithelial cells seem to exert a regenerative effort since they express trefoil proteins (pS2). The above mentioned properties give epithelial cells the leading role in the pathophysiology of the syndrome but the exact causative agent which drives the immune system towards an autoimmune reaction still remains obscure.